1. Field of the Invention
This invention relates to a novel organic compound, a liquid crystal composition containing the same, and to an optical switching element utilizing the composition as a liquid crystal. More particularly, it relates to an organic compound having an optically active group and being useful as a component of ferroelectric liquid crystal compositions, a ferroelectric liquid crystal composition containing the same, and an optical switching element utilizing the composition as a liquid crystal.
2. Description of the Related Art
At present, TN (Twisted Nematic) type display mode has been broadly employed for liquid crystal display elements. This TN liquid crystal display has many advantages such as lower driving voltage, less power consumption, etc. However, the display element is inferior in the aspect of response speed to emissive type display elements such as cathode ray tube, electroluminescence, plasma display, etc. A new TN type display element having the twist angle increased from 90.degree. as used in the conventional TN type liquid crystal display element to a range of 180.degree. to 270.degree. has also been developed, but it is still inferior in the aspect of response speed. As described above, various attempts for improvement have been made, but they have not yet been brought to practical use. Recently, however, a novel display mode using ferroelectric liquid crystals has been extensively researched, and according to such a mode, there is a possibility that the response speed is notably improved (Clark et al., Applied Phys. lett., 36, 899 (1980)). This mode is directed to a method of making use of chiral smectic phases such as chiral smectic C phase (hereinafter abbreviated to SC*) exhibiting ferroelectricity. Phases exhibiting ferroelectricity are not only SC* phase, alone, but it is known that chiral smectic phases of F, G, H, I, etc. also exhibit ferroelectricity.
Many specific features are required for practical use of ferroelectric liquid crystal materials in ferroelectric liquid crystal display elements, but at present there is no single compound which satisfies the requirements; hence, it is necessary to use a ferroelectric liquid crystal composition obtained by blending some liquid crystals or non-crystalline liquid crystal compounds.
Further, not only a ferroelectric liquid crystal composition consisting only of ferroelectric liquid crystal compounds, but also a ferroelectric liquid crystal composition has been proposed in Japanese patent application laid-open No. Sho 61-19518, which composition is obtained by blending at least one compound exhibiting a ferroelectric liquid crystal compound with compound(s) or a composition exhibiting an achiral smectic C, F, G, H, I or the like (hereinafter abbreviated to SC, SF, SG, SH, SI, etc., respectively) phase as basic substance(s) to give a ferroelectric liquid crystal composition as a whole. Still further, a ferroelectric liquid crystal composition has been reported in Mol. Cryst. Liq. Cryst., 89, 327 (1982), which composition is obtained by blending at least one compound which is optically active but exhibits no ferroelectric liquid crystalline phase with compound(s) or a composition exhibiting SC phase or the like as a main component to give a ferroelectric liquid crystal composition as a whole.
As a summary of these facts, it is seen that when at least one optically active compound, irrespective of whether or not this compound exhibits a ferroelectric liquid crystalline phase, is blended with smectic phase-exhibiting liquid crystal substance(s), it is possible to constitute a ferroelectric liquid crystal composition. Nevertheless, it is preferred that such an optically active substance also exhibit a liquid crystalline phase, and even when it exhibits no liquid crystalline phase, it is preferred to be a compound the structure of which is similar to those of liquid crystal compounds, so to speak a pseudo-liquid crystal substance.